Following on from our first article in the SAS series, NECA Technical has since received feedback from members relating to varying situations you've been facing.

The instance we wish to share with you relates to fault finding with a digital multimeter (DMM).

ScenarioA voltage of approximately 110 volts AC was found between an earth and neutral using a DMM set on volts.

The contractor spent considerable time splitting circuits, second guessing themselves and generally getting worked up. This was due to the fact that they could not identify where this voltage was coming from.

The reason for this voltage reading is due to capacitive coupling and is completely normal.

This happens when there is an active AC wire in parallel with an unconnected wire. Basically, time was wasted going on a wild goose chase, looking for a problem that was not there.

Solution

If you are going to use a DMM to fault find, make sure it has a LoZ (low impedance) function or use an analogue meter as they have internal low impedance circuitry.

The cost associated with purchasing a DMM with a LoZ function far outweighs the frustrations and time spent on site looking for voltages that do not exist.

If you have any questions about this SAS article please do not hesitate to contact NECA Technical via our Technical Hotline on 1300 6322 8324. If you would like to submit an SAS feature for a future edition of eNews, please email NECA Technical at technical@necawa.asn.au